Researchers exploring the mysteries of cat urine say there appear to be messages hidden in the stink. A study published Wednesday in Current Biology reports that a set of chemicals in feline urine, called branched-chain fatty acids (BCFAs), forms a stable scent “signature” that lets cats distinguish one another by smell alone, Live Science reports. Researchers observed that cats’ flehmen response—an open-mouthed sniff known to draw chemicals into the vomeronasal organ, which detects pheromones—dropped as they repeatedly smelled the same cat’s urine, but increased when urine from a different cat appeared.
When scientists separated urine into components, cats reacted specifically to the fatty-acid fraction, which was unique to each animal and stayed consistent for at least a day after a scent mark was left. Researchers identified 13 BCFAs, which appear in different combinations and proportions depending on the feline, acting as a chemical “calling card,” reports Popular Science. Interestingly, related cats had similar profiles, meaning family relations might be determined by a sniff. The chemicals appear to be stored in fat droplets in the kidney; big cats like lions and tigers use a similar system, suggesting it evolved across the feline family.